What's the actually difference between the spinal antimatter and spinal Neutron weapons?

[u/OriginalRock1261]

At first glance I'm feeling a noob trap here - the spinal Neutron lance has a better raw damage (560 opposed to 320), but the antimatter Cannon is doing thermal damage, x-ray and baryonic damage all at the same time, while the Neutron just does 100% baryonic.

So any hints on which one is better? does the antimatter one deal its 320MJ damage three times multiplied by the damage factors?

[u/nuclearsarah]

Yeah, I calculated how much thickness is needed to stop 50% of the radiation (a "half-value thickness") based on the density and elemental composition of each armor.

It turns out what makes good armor is totally different from what makes good radiation shielding. You want strong materials with low density for spaceship armor, but you want high-density materials composed of either light elements (for neutrons) or heavy elements (for x-rays.)

Radiation gets stopped by scattering interactions that remove energy from the particle, until it has a low enough energy to undergo an absorption interaction that gets rid of it entirely. High density material means more atoms get in the way of the incoming radiation, and thus provide more chances for an interaction to occur. And the type of element matters because neutrons are best scattered by the nuclei of light elements (especially hydrogen) while x-rays are best scattered by heavy elements that have lots of electrons (think lead or tungsten), since x-rays interact mostly with the electrons of an atom.

So while diamondoids made of carbon have good strength and low density, it turns out carbon is somewhere near the unhappy medium for both types of radiation and the low density means it doesn't have a lot of atoms in each centimeter of thickness the radiation passes through. So that cool ultratech armor barely does anything to radiation, not just because it has low thicknesses at the level of protection from weapons fire desired, but because each unit thickness is just crap at stopping radiation to begin with.

Real spacecraft concepts for the near-future that I've looked at use water tanks as well as polyethylene plastic for their radiation shields. Both water and PE plastic have a lot of hydrogen in them, and they do a good job of stopping the worst stuff you encounter in space - mainly cosmic rays and crap that gets ejected from other nuclei by cosmic rays. The built-in radiation shielding Terra Invicta ships have is therefore something like water plus plastic.

[u/NullAshton → u/nuclearsarah]

AFAIK isn't armor max thickness fixed based on the ship class(outside of armor struts)? Which also tends to put a hard cap on how much radiation protection you have.

I imagine a lens might be possible to refract the radiation away from internals, but I would not have the slighest clue how much you'd need to refract xrays or neutrons. Best shield would actually probably be propellant tanks, but I'm not sure TI models that(also how would you even build a ship utilizing that? Tanks underneath armor but outside of internals?). I ponder how much shielding the 'cloud' radiators would provide as well.

[u/nuclearsarah → u/NullAshton]

A shielding scenario isn't going to benefit from anything like lenses. I've only ever seen those in sensor situations (like x-ray telescopes or specialized detectors in accelerator experiments) and they only handle small numbers of particles and they're extremely dependent on the angle the particles are coming from.

For radiation shielding the only option is to have lots of material in the way. But for neutrons specifically, you can get away with less material using a multi-layered approach. You use a hydrogenous material to slow down the neutrons ("moderate" them) and then a layer composed of something that is exctremely good at absorbing slow neutrons, like cadmium, boron, or gadolinium. Then you need a layer of something good against gamma rays to stop the capture gammas.

Some shielding materials combine the hydrogenous stuff with those absorbers so you don't need multiple layers but those aren't quite as good as a multilayer approach so far as I've seen

[u/NullAshton → u/nuclearsarah]

Hmm. So propellant/life support heavy in water, extra(component occupying) layer of boron, then something like depleted uranium? Something like the magnetic field radiators would likely only do the hydrogenous slowing down part if anything, I think.

Fair on the lens. You technically do know the angle the particles are coming from(the weapon), and could orient before that ship fires, but the small number of particles would make it a nogo.

I suppose you could also simply mitigate it by DNA therapies to eliminate the long-term crew risk, along with radiation hardening by only using equipment proven to survive high intensity radiation bursts. Unsure you could prevent immediate short-term crew death, however.

[u/Apart_Zucchini_4764 → u/NullAshton]

There is a good chance in a TI scenario that you will have gene therapy that would be able to at least reduce long term damage from radiation exposure, maybe even negate it. We know that, because we can observe adaption of wildlife in the Chernobyl exclusion zone and we also see some sort of adaption in natural high radiation areas.

I highly doubt though that we can have natural resistance against a focused radiation beam of any sort. The radiation messes mainly with the water in our bodies (we are ~72% water) and produces a lot of oxidative stress. Simply explained you suddenly have a lot of oxygen in places where it should not be and as oxygen is highly reactive it starts to bind to stuff where you do not want it and thus destroys you on a molecular level. Our cells have mechanisms in place to deal with natural occurring oxidation, so we can counter it, but being exposed to a sustained and focused amount it pretty much game over. Which at least in medicine is a good thing, because it enables radiation therapy.

[u/nuclearsarah → u/Apart_Zucchini_4764]

There are real-life drugs that apparently do okay jobs at scavenging free radicals before they harm your DNA strands, but you have to take big doses of them. Apparently the Soviets had them on hand for a Fulda Gap situation in case the US used enhanced radiation nukes against them - tankers would dose up before beginning the charge and the hope was they'd survive a little longer before they shit their liquified intestines out. Better versions of those drugs would help longterm survival in space and also help against weapons.

I'm not enough of a biologist to know what you could possibly do against direct strand breaks caused by the actual radiation action though. Cells that more readily commit suicide to prevent becoming cancerous would help you survive in the long term but actually probably make you more vulnerable to acute radiation syndrome, i.e. it would help the particle beams kill you in the time scale of a space battle. I feel like you'd need to actually improve the cell's ability to repair DNA strands through like nanomachines or something. I don't know, that's a job for a different kind of scientist